I posted in another thread that I don't totally understand QBR (its not the traditional "QB rating") but they claim its a better gauge of a QB's effectiveness (or lack of)
That said, yesterday Trevor Lawrence had a game in which his team was shutout and he finished with 0 tds and 4 picks. His QBR for that game was 18.9. He was 24/40 for 221 yards, and as mentioned 0 tds and 4 picks.
He wasn't anywhere near the worst for QBR yesterday. The 3 worst?
Taylor Heinicke: 11/25 122 yrds, 1 TD and 1 pick. QBR of 4.9
Teammate: Kyle Allen 4/9 53yds, 0 tds and 0 picks 5.8
Dak Prescott: 22/39 211 yrds, 1 td and 2 picks. QBR of 9.9
That means that of the QB's who started and finished a game yesterday ACROSS the league, Prescott had the worst game of any QB.